Abstract : The supplemental aeration of the (Rotating Biological Contactor) system eliminated nuisance organisms, enhanced (Biological Oxygen Demand 5-S) and NH3-N removal, and provided the operational flexibility to control the thickness of biomass growth on the media. Placement of air diffusers in not only BOD5-S removal stages, but also in NH3-N removal stages should be maintained at 2.5 mg/L in stages where maximum nitrification rates are expected.